The present invention relates to an image forming apparatus, such as a copy machine or a printer, which uses electrophotography.
As an image forming apparatus of this type, there is an apparatus for forming an electrostatic latent image on a photosensitive drum, and supplying the latent image with a non-magnetic mono-component developer to develop it, using a developing roller. The developing roller abuts against a layer-thickness-limiting member. This member enables the formation, on the developing roller, of a layer of the non-magnetic mono-component developer having a predetermined thickness. The photosensitive drum comprises, for example, an aluminum tube and a photosensitive layer provided on the outer periphery of the tube.
In order to develop an electrostatic latent image in a good condition, it is necessary to secure a sufficient nipping force at a contact portion between the photosensitive drum and the developing roller.
To this end, in the prior art, the base material of the photosensitive drum is formed of an aluminum tube, the developing roller is formed of an elastic rubber member, and the layer-thickness-limiting member is formed of a layer-thickness-limiting metal blade having elasticity.
However, in providing a sufficient nipping force at the nipping portion between the developing roller and the layer-thickness-limiting blade where the developing roller is formed of an elastic rubber member, frictional heat created at the nipping portion inevitably accumulates in the elastic developing roller. As a result, the developer may adhere to the layer-thickness-limiting blade and/or the developing roller, thereby disrupting development.
On the other hand, there is a conventional image forming apparatus using electrophotography, which employs a metal developing roller and a photosensitive belt formed of a high polymer film such as polyester (PET), as a base material. Further, the layer-thickness-limiting blade is formed of a plate spring or a plate spring coated with, for example, urethane resin chips. The developing roller employed in this conventional case is made of a metal and therefore has a high thermal conductivity and dissipation quality.
In this case, however, the base material of the photosensitive belt is polyester (PET), and therefore the photosensitive belt has a low thermal conductivity and dissipation quality. This being so, frictional heat created at the contact portion between the layer-thickness-limiting blade and the developing roller accumulates in the developing roller, with the result that the developer may adhere to the layer-thickness-limiting blade and/or the developing roller, thereby disrupting development.
The present invention has been developed in light of the above-described circumstances. In the image forming apparatus of the invention, a developing roller, a thickness-limiting blade and a base material of a photosensitive belt are each made of a metal, and thus the frictional heat generated at the contact portion between the developing roller and the thickness-limiting blade is effectively transmitted to the photosensitive belt to be dissipated.
Accordingly, an increase in the temperature of each developing unit can be prevented, thereby preventing the adhesion of toner to the developing roller and/or the thickness-limiting blade, and hence enabling good development.
Further, when using a thickness-limiting metal roller as the thickness-limiting member, a higher temperature increase suppressing effect can be obtained, since the heat dissipation area of the roller is larger than that of a blade-type thickness-limiting member.
Also, since the developing roller of each developing unit is brought into contact with the photosensitive belt after the image forming process, the effect of dissipating the heat of each developing unit can be enhanced.
In addition, since a cooling fan cools the photosensitive belt, an increase in the temperature of each developing unit can be more reliably suppressed.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.